I hope they make a standard XML based application manager. This will not change how older software installs. But, I hope some right minded developer would follow this standard application manager installation.
Basically it is like Gadget install. NO installer!!!! NO uninstaller!!!!. Because even Yahoo and Google failed to make a proper uninstaller and they are so annoying. Run uninstaller and nothing really uninstalled. If it is completely managed by Windows, I wouldn't have this evil developer making crap uninstaller problems.
Certainly this is not a mandatory way to install a software, because application manager should have limited flexibility. Thus, users can expect certain safty from it, like installing something won't damage IE or FF because the managere doesn't allow it to change other program space.